/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.parsing;

import org.springframework.lang.Nullable;

import java.util.LinkedList;

/**
 * Simple {@link LinkedList}-based structure for tracking the logical position during
 * a parsing process. {@link Entry entries} are added to the LinkedList at
 * each point during the parse phase in a reader-specific manner.
 *
 * <p>Calling {@link #toString()} will render a tree-style view of the current logical
 * position in the parse phase. This representation is intended for use in
 * error messages.
 *
 * @author Rob Harrop
 * @since 2.0
 */
public final class ParseState {

    /**
     * Tab character used when rendering the tree-style representation.
     */
    private static final char TAB = '\t';

    /**
     * Internal {@link LinkedList} storage.
     */
    private final LinkedList<Entry> state;


    /**
     * Create a new {@code ParseState} with an empty {@link LinkedList}.
     */
    public ParseState() {
        this.state = new LinkedList<>();
    }

    /**
     * Create a new {@code ParseState} whose {@link LinkedList} is a {@link Object#clone clone}
     * of that of the passed in {@code ParseState}.
     */
    @SuppressWarnings("unchecked")
    private ParseState(ParseState other) {
        this.state = (LinkedList<Entry>) other.state.clone();
    }


    /**
     * Add a new {@link Entry} to the {@link LinkedList}.
     */
    public void push(Entry entry) {
        this.state.push(entry);
    }

    /**
     * Remove an {@link Entry} from the {@link LinkedList}.
     */
    public void pop() {
        this.state.pop();
    }

    /**
     * Return the {@link Entry} currently at the top of the {@link LinkedList} or
     * {@code null} if the {@link LinkedList} is empty.
     */
    @Nullable
    public Entry peek() {
        return this.state.peek();
    }

    /**
     * Create a new instance of {@link ParseState} which is an independent snapshot
     * of this instance.
     */
    public ParseState snapshot() {
        return new ParseState(this);
    }


    /**
     * Returns a tree-style representation of the current {@code ParseState}.
     */
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (int x = 0; x < this.state.size(); x++) {
            if (x > 0) {
                sb.append('\n');
                for (int y = 0; y < x; y++) {
                    sb.append(TAB);
                }
                sb.append("-> ");
            }
            sb.append(this.state.get(x));
        }
        return sb.toString();
    }


    /**
     * Marker interface for entries into the {@link ParseState}.
     */
    public interface Entry {

    }

}
